The goals of this project are to study the neural and cellular bases of labyrinthine function in the fish as they relate to equilibrium and hearing. Toadfish, Opsanus tau will provide a model system. We will use video microscopy and image analysis techniques to study cupular mechanics and micromechanics in response to adequate stimulation to evaluate possible cupular contributions to the shaping of afferent responses and will model the actual cupula-endolymph system of toadfish. We will study receptor currents in response to stereociliary movement in hair cells located in the center and periphery of the crista. Efferent effects upon centrally and peripherally located hair cells will also be documented. We plan parallel studies of saccular and utricular function. The brainstem and labyrinth of toadfish ar relatively well studied. In fish, sound is transduced by hair cells of one or more of the otolithic organs that act as auditory receivers to operate within the appropriate frequency spectrum. We will employ techniques developed in semicircular canal studies to investigate the hearing organs of fish. These include chronic and acute recording and morphophysiological studies of central and peripheral projections of primary afferent. We will assess the role of the saccule and utricle in sound reception by recording from their afferent during sound stimuli. The central projections of the putative sound receiving organs, primarily the saccule and utricle, occupy areas of the anterior octavus nucleus that is relatively free of vestibular input. We will continue morphological studies to delineate auditory from vestibular brainstem areas. The central and peripheral morphology of single afferent will be studied to determine if there are specific receptor organ regions that process sound versus vestibular sensation and to specify possible common areas of the brain that process sound.